pub fn dp_rec_mc(mut amount: u32) -> u32 {
    [100, 50, 30, 20, 10, 5, 2, 1]
        .into_iter()
        .filter_map(|bill| {
            if amount == 0 {
                return None;
            }
            let count = amount / bill;
            amount %= bill;
            Some(count)
        })
        .sum()
}
